Conventionally, a position detection apparatus that detects a position of a moving body such as a servo motor or the like attached to a machine moving part in a machine tool or the like by detecting changes in a physical quantity caused by rotational movement or the like of the moving body has been used. Through the output from this position detection apparatus, the rotational movement or the like of the moving body is continuously tracked, and by providing feedback to the moving body, movement control of the moving body is accomplished.
As this kind of position detection apparatus, an apparatus that is provided with a magnetic field generation part for generating a magnetic field and a magnetic detection apparatus is known. This magnetic detection apparatus, in general, is provided with a magnetic detection element, which detects an external magnetic field generated by the magnetic field generation part and outputs an analog signal indicating a physical quantity that the magnetic field generation part has relatively moved, and a calculation circuit, which can convert the analog signal into a digital signal and compute the position of the moving body at the present time based on this digital signal. This magnetic detection apparatus is configured as an integrated circuit in which the magnetic detection element and the calculation circuit are integrated on the same semiconductor chip.
Movement control of the moving body is accomplished based on the position information of the moving body at the present time computed in the calculation circuit of this magnetic detection apparatus. However, delays can arise from the filtering process for the analog signal output from the magnetic detection element, the process of converting the analog signal into a digital signal, the filtering process for removing noise included in this digital signal and the process of computing the position of the moving body at the present time based on the digital signal. Consequently, particularly to precisely control movement of a moving body operating at high speed and to make up for the delay, a method that forecasts the position of the moving body at a future time from the position information of the moving body and controls the moving body on the basis of this forecasted value is adopted.
As a position detection apparatus capable of implementing this kind of method, conventionally, a rotation detection apparatus that includes a magnetic sensor element that measures the magnetic field strength of magnets provided in a rotating body, an angle calculation means for calculating the rotation angle of the magnets from the measured value of the magnetic sensor element, a storage means for storing the data of the rotation angle output from the angle calculation means, a rotational state estimation means for estimating the rotational state through statistical processing of the contents stored in the storage means, an extrapolation processing means for forecasting later rotational angles from the rotational state estimated by the rotational state estimation means, and an output means for calculating and outputting a rotational angle based on the rotational angle forecast by the extrapolation processing means have been proposed. (see Patent Literature 1).